Signal transmitter

ABSTRACT

A signal transmitter for transmitting the international distress signal which includes a generator for simultaneously producing the military and civil distress signals having the appropriate frequencies. An antenna is provided which is tuned to a frequency intermediate the military and civil signal frequencies. An impedance matching network is connected between the antenna and the generator which is adapted to produce the conjugate impedance of the antenna at the military and civil signal frequencies so that the signals are transmitted with substantially maximum power.

FIPBlOE Glatzer et al. 1 May 23, 1972 [54] SIGNAL TRANSMITTER 3,174,103 3/1965 Monroe 25/153 x 72 Inventors: Stephen G. Glatzer, 541 Pelham Road, 5:32? ,22? New Rochelle, NY. 10805; Rocco ScaP- 2989626 M961 g "24 X g g b gg Terrace Mamammk 3,176,229 3/1965 Pierce ..325/105 [22] Filed: Sept. 3, 1969 Primary Examiner-David L. Trafton pp No: 854,882 Attomey-Meyer A. Gross 57 ABSTRACT [52] 7 2 A signal transmitter for transmitting the international distress l 343/894 331/47 signal which includes a generator for simultaneously produc- I Cl 6 loo ing the military and civil distress signals having the apg i 153 160 propriate frequencies. An antenna is provided which is tuned 1 e o 5 6 5 to a frequency intermediate the military and civil signal frequencies. An impedance matching network is connected 56 R f and between the antenna and the generator which is adapted to I 1 e erences I produce the conjugate impedance of the antenna at the milita- UNITED STATES PATENTS ry and civil signal frequencies so that the signals are transmitted with substantially maximum power, 2,855,508 10/1958 Barlow et al ..325/178 X 1,523,011 1 1925 Garity ..325 124 11 Claims,2DrawingFigures pmwmn This invention relates-generally toa signal transmitter and, more, particularly, pertains to a transmitter for generating and broadcastinga distress signal.

As is well known to fliers, sailors, servicemen, adventurists and the like, the international emergency distress signal is a wobbling tonewhich may be transmitted at a military carrier frequency of 243 MHz or a civil carrier frequency of l2l.5 MHz. Presently, there are a number of commercially available signal'transmitters which are specifically designed for useby the above-noted classes of people or, for that matter, any person-likely to encounter sudden emergency conditions. However, these devices suffer from a number of various drawbacks which seriously limit their overall usefullness.

For example, one particular disadvantage is that many such transmitters do not have a separate power supply and consequently draw power from the power source which drives the vehicle in which they are travelling. Accordingly, if this power source is destroyed, as in a crash or the like, the transmitter is rendered useless. Even if the power source remains intact, these types of transmitters have been found to deplete. such power sources within -15 minutes of continuous use. When it is taken into-consideration that it normally takes approximately 55 minutes to locate an emergency or distress signal transmitter, it becomes obvious that the use of such transmitters as emergency devices is, at best, questionable.

Other types of distress signal transmitters are portable to the extent that they incorporate self-contained power supplies; however, these transmitters similarly have drawbacks associated with their use. Thus, in practice it has been that the shelf-life of the portable power supply is relatively short. Hence, when the transmitter is called upon toperform it may only produce a signal for an insufficiently short interval of time. Even if the power supply has a long shelf-life but has not. been renewed at proper intervals, the same result will be obtained. Since present portable transmitters of the type under consideration do not incorporate any means to notify the operator that the power source is depleted, the person in distress usually falsely relies upon the transmitter, to his detriment.

Other problems associated with prior art distress signal transmitters of the aforementioned types arise because variable elements are utilized in the tuned circuits incorporated in the transmitter. As a result, tuning procedures are necessary to initially tune the transmitters to the desired carrier frequency thereby increasing the overall cost of such devices in terms of both the cost of such elements and the labor involved in such critical tuning procedures.

Accordingly, a general object of the present invention is to provide an improved emergency or distress signal transmitter.

A more specific object of the invention is to provide portable distress signal transmitter having a self-contained long-life power supply.

A further object of this aspect of the present invention is the provision of a signal generator having a built-in test apparatus to quickly' notify the operator as to whether the transmitter is operable or inoperable.

Another object of this invention resides in the novel details of the circuitry which provide a transmitter of the type described which does not utilize variable elements in the tuned circuits thereby eliminating the problems and added costs which are associated with such elements.

A further object of the invention is to provide a reliable and inexpensive transmitter which broadcasts the international distress signal at both military and civil carrier frequencies simultaneously.

Accordingly, a distress signal transmitter constructed according to the. present invention comprises signal generator means for generating first and second signals wherein the second signal has a higher frequency than the first signal. An antenna is provided which has a wavelength appropriate for the transmission of a signal having a wavelength intermediate the wavelength of said first and second signals. Impedance matching means is connected between the signal generator means and the antenna for producing the respective conjugate impedances of said antenna at said first and second signals.

Other features andadvantages of the-present invention will become more apparent from a consideration of the following detailed description when taken in conjunction. with the accompanying drawing, in which:

FIG. 1 is a schematic circuit wiring diagram of a distress signal transmitter constructed according to the present invention; and

FIG. 2 is a bottom plan view of a printed circuit board illustrating coils which may be used in the circuit of FIG. 1. a

As noted hereinabove, the signal transmitter of the present invention is operable to broadcast the international distress or emergency signal on the military carrier frequency of 243.0 MHz and the "civil carrier frequency of 121.5 MHz. These carrier frequencies are amplitude modulated with a signal which sweeps through a range of from 300 Hz to 1,000 Hz at a 2-3 Hzrate to produce the wobbling tone which is indicative of the emergency signal.

Accordingly, a transmitter constructed according to the present invention is designated generally by the reference numeral 10 in FIG. 1 and includes a grounded base crystal oscillator transistor stage 12. More specifically, the stage 12 includes a transistor 14 having a base electrode 16 connected to ground through a crystal 18. A resistor 20 is connected in parallel with the crystal 18. Connected to the collector electrode.22 of the transistor 14 is one end of a tuned or tank circuit comprising a'capacitor 24 and an inductor 26. The other end of the capacitor 24 is connected to ground and the other end of the inductor 26 is returned to the base electrode 16 via a resistor 28. The emitter electrode 30 of the transistor 14 is connected to ground through a resistor 32 and to a tap on the inductor 26 through a capacitor 34. Connected to the junction of the inductor 26 and the resistor 28 is a by-pass capacitor 36. Also-connected to this junction is one end of a resistor 38, the other end of which is connected to a. power lead 40 which, in turn, is connected to the positive terminal of a biasing source 42. As shown in FIG. 1, the source 42 may comprise a battery pack.

in the example under consideration, the oscillator stage 12 is tuned to and produces a 60.750 MHz signal. This signal is applied to a high efficiency frequency doubler stage 44 through a coupling capacitor 46, one end of which is connected to an appropriate tap on the inductor 26.

More particularly, the stage 44 includes a transistor 48, the base electrode 50 of which is connected to the other end of the capacitor 46. Additionally, the electrode 50 is connected to a modulating circuit, which is designated generally by the reference numeral 52 and is described in detail below, by a lead 54 through a resistor 56 A by-pass capacitor 58 is connected between the end of the resistor 56 remote from the electrode 50 and ground. The emitter electrode 60 of the transistor 48 is connected to ground. The collector electrode 62 of the transistor 48 is connected to the power'lead 40 through a series circuit comprising an inductor 64 and a resistor 66. A tuning capacitor 68 is connected between the electrode 62 and ground and, together with the inductor 64, forms a tuned or tank circuit. A by-pass capacitor 70 is connected between the junction of resistor 66 and inductor 64 and ground. a

The output signal of the stage 44 is applied to another frequency doubler stage 72 through a coupling capacitor 74 having one end connected to an appropriate tap on the inductor 64. As noted above, in the example under consideration, the oscillator stage produces a signal having a frequency of 60.750 MHz. Hence, the frequency of the signal appearing at the output of the stage 48 will be 121.5 MHz. In other words the tuned circuit comprising the inductor 64 and the capacitor 68 is tuned to 121.5 MHz.

The stage 72 includes a transistor 76, the base electrode 78 of which is connected to the other end of the capacitor 74 and to ground through a resistor 80. The emitter electrode 82 of the transistor 76 is connected to ground and the collector electrode 84 thereof is connected to one end of an inductor 86. The other end of the inductor 86 is connected to a junction 88 to which is connected one end of another inductor 90. The other end of the inductor 90 is connected to the power lead 40 and to one end of a by-pass capacitor 92, the other end of which is connected to ground.

While no physical tuning capacitor per se is used to tune the inductors 86 and 90, use is made of the collector-to-emitter capacitance (i.e., the varactor effect of the transistor 76) to produce the desired signal. Moreover, the parameters of the stage 72 are chosen so that the signal of fundamental frequency (i.e., the frequency of the input signal) and the second harmonic signal appearing between the junction 88 and ground have equal amplitudes. Thus, in the specific example under consideration, two substantially equal amplitude signals will appear between the junction 88 and ground; one signal having a frequency of 121.5 MHz, and the other signal having a frequency of 243 MHz.

Connected to the junction 88 is one end of a signal trap 94 comprising an inductor 96 and a capacitor 98 connected in parallel therewith. The other end of the trap 94 is connected to an antenna lead 100 through a coupling capacitor 102. The lead 100 is connected to a telescoping dipole antenna 104.

in practice the trap 94 is tuned to reject the third harmonic of the oscillator frequency or, in the circuit under consideration, the trap 94 rejects signals having frequencies of approximately 180.0 MHz but passes the 121.5 MHZ and 243 MHz signals to the antenna 104 via the capacitor 102 and the lead 100. It will now be obvious that the circuit thus far described simultaneously produces the military emergency carrier frequency signal of 243 MHz and the civil emergency carrier frequency signal of 121.5 MHz and transmits the same via the antenna 104.

Since it is desirable to transmit or broadcast both of the above signals with substantially full power, a feature of the invention is to provide a novel impedance matching arrangement at both of the aforementioned frequencies. Thus, the antenna 104, when extended, is selected to be slightly short at the wavelength corresponding to the signal of l2l.5 MHz. Hence, the antenna 104 appears to have a capacitive reactance at 121.5 MHz and an inductive reactance at 243.0 MHz. However, the trap 94 is tuned to 180 MHz. Hence, the trap 94 exhibits an inductive reactance at 121.5 MHz and a capacitive reactance at 243 MHz. Thus, in view of the fact that the impedances of the antenna 104 and the trap 94 are the conjugate of each other at the two frequencies of interest, the antenna is matched to the circuit and the two carrier signals are broadcast with substantially no attenuation due to mismatching.

Thc modulating circuit 52 is adapted to amplitude modulate the l2l.5 MHz and 243 MHz signals at a 2-3 Hz rate with a signal which sweeps from 300 Hz to 1,000 Hz. Accordingly, the modulating circuit 52 includes a unijunction transistor 106 the first base electrode 108 of which is connected to ground and the second base electrode 110 of which is connected to the power lead 40 through a resistor 112. The emitter electrode 114 of the transistor 106 is connected to the junction 116 ofa resistor 118 and a capacitor 120. The other end ofthe capacitor 120 is connected to ground and the other end of the resistor 118 is connected to the lead 40.

The operation of unijunction transistor 106 is conventional. Thus, the potential across the capacitor 120 begins to increase until the triggering potential of the transistor 106 is reached at which point the transistor conducts and the capacitor 120 discharges therethrough. Accordingly, a sawtooth waveform is generated across the capacitor 120 and the parameters are chosen so that this sawtooth potential has a frequency of approximately 3 Hz.

Connected between the junction 116 and ground is a voltage divider network comprising the serially connected resistors 122 and 124. The base electrode 126 of a transistor 128 of a phase inverter stage is connected to the junction of the resistors 122 and 124. The emitter electrode 130 of the transistor 128 is connected to ground through a resistor 132 and the collector electrode 134 thereof is connected to the power lead 40 through a resistor 136.

The anode electrode of a diode 138 is connected to the collector electrode 134 of the transistor 128 and the cathode electrode thereof is connected to the junction 140 of an RC circuit comprising a resistor 142 connected between the lead 40 and the junction 140, and a capacitor 144 connected between the junction and ground.

Also connected to the junction 140 is the emitter electrode 146 of a unijunction transistor 148. The first base electrode 150 of the transistor 148 is connected to ground and the second base electrode 152 is connected to the lead 40 through a resistor 154. The signal appearing between electrode 146 and ground sweeps between 1,000 and 300 Hz at a 3 Hz rate.

To be more specific, the conduction of the phase inverter stage or transistor 128 will vary at substantially a 3 Hz rate under control of the sawtooth signal appearing at the junction 1 16. When the transistor 128 is fully conducting the capacitor 144 charges through the resistor 142 until the triggering potential of the unijunction transistor 148 is reached. The elements are chosen so that the signal produced occurs at a 300 Hz rate for this condition of the transistor 128. However, when the transistor 128 is in cut-off, the diode 138 is biased to conduct thereby connecting the resistor 136 in parallel with the resistor 142 to change the effective resistance and, therefore, the time constant of the charging circuit. For this condition of the circuit the elements are chosen so that the signal appearing across the capacitor 144 occurs at a 1,000 Hz rate. For intermediate values of conduction of the transistor 128 the effective resistance in series with the capacitor 144 will vary accordingly. Hence, the signal appearing on the electrode 146 of the unijunction transistor 148 will sweep from 300 to 1,000 Hz at the 3 Hz rate.

Connected to the electrode 146 is the base electrode 156 of a transistor 158. The emitter electrode 160 of the transistor 158 is connected to ground through a resistor 162 and the collector electrode 164 is connected to the lead 54 through a resistor 166. Additionally, the electrode 160 is connected to the lead 40 through a resistor 168.

In operation, the transistor 158 operates as a switch which opens and closes at a rate determined by the waveform on the base electrode 156. Thus, when the transistor 158 is conducting, the resistor 56, which is in the base circuit of the frequency doubler stage 44, is essentially connected to ground. However, when the transistor 158 is in cut-off the end of the resistor 56 remote from the electrode 50 is floating thereby causing the transistor 48 to cease conducting. Thus, the action of the transistor 158 is to amplitude modulate the signal applied to the stage 44 from the oscillator stage 12. Hence, the output 121.5 MHz and the 243 MHz signals will be amplitude modulated by a signal which sweeps through a frequency band offrom 300 Hz to 1,000 Hz at approximately a 3 Hz rate.

The operation of the transmitter 10 is controlled by a pair of ganged single-pole triple throw switches and 172. To be more specific, the respective armatures 170A and 172A of the switches 170 and 172 are connected together and to ground by a lead 174. The terminals 172B, 172D and 1708 of the respective switches are connected together and to the negative terminal of the source 42 by a lead 176. The terminals 172C and 170C are unconnected while the terminal 170D of the switch 170 is connected to the antenna lead 100 through a test lamp 178.

Under normal circumstances the armatures 170A and 172A of the respective switches 170 and 172 will be in contact with the terminals 170C and 172C, respectively. When it is desired to operate the transmitter the telescoping antenna 104 is pulled out to its required length and the ganged switches are operated to the lower position so that the respective armatures engage the contacts 170B and 1728. Thus, the negative terminal of the source 42 will be grounded through the lead 176 and the respective switches to complete the circuit between the energy source 42 and the appropriate elements. Accordingly, the transmitter will broadcast the necessary distress signals on both the military and civil frequency bands in the manner described above. I

As noted above, a feature of the present invention is to provide means for quickly and easily determining whether the transmitter 10 is operational without the needto broadcast false distress signals; Thus, when it is desired to test the transmitter the switches 170, 172 are operated to connect the armatures 170A, 172 to the respective terminals 170D, 172D. At this time the telescoping antenna 104 is left in the collapsed position. The source 42 will be grounded through the lead 176 and the switch 172 so that the distress signals will be generated. However, the collapsed antenna 104 will limit the broadcast of the signals to a relatively small range.

Additionally, the test lamp 178 will be connected between the antenna lead 100 and ground via the switch 170. Hence, the output distress signals similarly will be applied to the lamp 178. Since the output signals are AM carrier signals, the lamp 178 will flicker at a rate determined by the modulated envelope of the carrier wave. Accordingly, when the operator observes such flickering he is aware that the transmitter is operating properly. However, if the flickering is absent the operator is made aware that the device is faulty and should be replaced or repaired before embarking on the potentially hazardous journey.

It is to be noted that the'circuit of FIG. 1 utilizes solid state devices which consume minimum power. Hence, the source 42 may comprise an alkaline battery which ideally has a relatively long shelf-like to ensure proper operation of the transmitter 10 for a relatively long period of time. Additionally, the low power drain of the elements contributes to the long duration of signal broadcasting of the transmitter when it is operational.

It is further to be noted that the circuit of FIG. 1 does not use any variable tuning elements in the tuned circuits. To be more specific, use is made of the depletion capacitance of the transistors to eliminate the need for variable tuning elements and their consequent time consuming critical adjustments. For example, the elements 26 and 24 comprising the tuned circuit in the oscillator stage 12 are chosen so that the circuit resonates at the desired frequency. However, as a result of stray and wiring capacities, or tolerance variations in the components and the like, the circuit may resonate of at a slightly different frequency than 60.750 MHz. If the tuned circuit is off resonance, the current through the transistor 14 will decrease thereby changing the width of the depletion layer in the transistor and, hence, the junction or depletion capacitance exhibited by the transistor. Thus, the capacitance of the transistor changes automatically until resonance is obtained thereby eliminating the need for variable elements.

A further feature of the present invention is the provision of a printed circuit board on which the elements comprising the circuit of FIG. 1 are mounted and on which the inductor components are printed thereby eliminating the need for inductor elements and their consequent cost. Thus, as shown in FIG. 2, a printed circuit board 180 is provided which includes an insulating board 182. Printed on the underside of the board 182 are conductors 184 representing the various circuit connections. Also printed on the undersurface of the board 182 are coils such as coils 26 and 64 which are, in effect, inductors having the proper inductance, Q, etc. for their intended purpose. (it is to be noted that many conductors 184 and other circuit elements have not been shown in F lG. 2 in the interests of clarity.) The actual printing is performed in the conventional manner. Accordingly, as noted above, the need for physical inductors is eliminated.

Thus, a distress or anemergency signal transmitter has been disclosed which simultaneously broadcasts on both military and civil frequencies which is simple to fabricate and which is efficient and reliable in operation.

While a preferred embodiment of the invention has been shown and described herein it will become obvious that numerous ommissions, changes and additions may be made in such embodiment without departing from the spirit and scope of the present invention.

What is claimed is:

l. A signal transmitter comprising signal generator means for simultaneously generating a first and a second signal wherein the second signal has a higher frequency than said first signal, an antenna having a wave length corresponding to the wave length of a signal intermediate the wave lengths of said first and second signals, and a fixed frequency impedance matching means between said signal generator means and said antenna for producing the respective conjugate impedances of said antenna at said first and second signals.

2. A signal transmitter as in claim 1, in which said impedance matching means includes means tuned to reject a signal having a frequency intermediate the frequency of said first and second signals.

3. A signal transmitter as in claim 1, in which said signal generator comprising means for generating a fundamental frequency signal, the second harmonic of said fundamental frequency signal which corresponds to said first signal, and the fourth harmonic of said fundamental frequency signal which corresponds to said second signal; and said impedance matching means comprises a parallel inductor and capacitor circuit which is tuned to reject the third harmonic of said fundamental frequency signal.

4. A signal transmitter as in claim 1, and test means selectively connectable with said antenna and responsive to the amplitude modulation of said first and second signals for indicating such amplitude modulation.

5. A signal transmitter as in claim 4, in which said test means comprises a lamp, and a switch for connecting said lamp with said antenna.

6. A signal transmitter as in claim 1, in which said signal generator means comprises carrier frequency generating means for simultaneously producing first and second carrier frequency signals, said carrier frequency generating means including a frequency doubler stage operable to produce a fundamental and a second harmonic signal of substantially equal amplitudes whereby said second carrier frequency signal is twice the frequency of but substantially equal in amplitude to said first carrier frequency signal.

7. A signal transmitter as in claim 6, in which said frequency doubler stage includes a plurality of inductors, said inductors comprising a plurality of coils printed on a printed circuit board.

8. A signal transmitter as in claim 6, in which said signal generator means further comprises modulating means for modulating said first and second carrier frequency signals to produce said first and second signals, said modulating means being operable to modulate said first and second carrier frequency signals with a modulating signal which sweeps between a third and a fourth frequency at a predetermined rate.

9. A signal transmitter as in claim 8, in which said modulating means includes first signal means for producing a signal which varies at said predetermined rate, second signal means for producing a signal which sweeps between said third and fourth frequencies, and connecting means for connecting said first signal means with said second signal means to control the operation of said second signal means at a rate determined by said first signal means signal. I

10. A signal transmitter as in claim 9, in which said second signal means comprises a capacitor, discharging means connected in parallel with said capacitor for discharging said capacitor when the potential across said capacitor reaches a preselected value, a first charging resistor connected between said capacitor and a charging source for causing said capacitor to charge at a selected rate, a second charging resistor, and switch means responsive to said first signal means signal for selectively connecting said second resistor in parallel with saidfirst resistor to change the charging rate of said capacitor.

11. A signal transmitter as in claim 10, in which said switch means comprises a semiconductor diode. 

1. A signal transmitter comprising signal generator means for simultaneously generating a first and a second signal wherein the second signal has a higher frequency than said first signal, an antenna having a wave length corresponding to the wave length of a signal intermediate the wave lengths of said first and second signals, and a fixed frequency impedance matching means between said signal generator means and said antenna for producing the respective conjugate impedances of said antenna at said first and second signals.
 2. A signal transmitter as in claim 1, in which said impedance matching means includes means tuned to reject a signal having a frequency intermediate the frequency of said first and second signals.
 3. A signal transmitter as in claim 1, in which said signal generator comprising means for generating a fundamental frequency signal, the second harmonic of said fundamental frequency signal which corresponds to said first signal, and the fourth harmonic of said funDamental frequency signal which corresponds to said second signal; and said impedance matching means comprises a parallel inductor and capacitor circuit which is tuned to reject the third harmonic of said fundamental frequency signal.
 4. A signal transmitter as in claim 1, and test means selectively connectable with said antenna and responsive to the amplitude modulation of said first and second signals for indicating such amplitude modulation.
 5. A signal transmitter as in claim 4, in which said test means comprises a lamp, and a switch for connecting said lamp with said antenna.
 6. A signal transmitter as in claim 1, in which said signal generator means comprises carrier frequency generating means for simultaneously producing first and second carrier frequency signals, said carrier frequency generating means including a frequency doubler stage operable to produce a fundamental and a second harmonic signal of substantially equal amplitudes whereby said second carrier frequency signal is twice the frequency of but substantially equal in amplitude to said first carrier frequency signal.
 7. A signal transmitter as in claim 6, in which said frequency doubler stage includes a plurality of inductors, said inductors comprising a plurality of coils printed on a printed circuit board.
 8. A signal transmitter as in claim 6, in which said signal generator means further comprises modulating means for modulating said first and second carrier frequency signals to produce said first and second signals, said modulating means being operable to modulate said first and second carrier frequency signals with a modulating signal which sweeps between a third and a fourth frequency at a predetermined rate.
 9. A signal transmitter as in claim 8, in which said modulating means includes first signal means for producing a signal which varies at said predetermined rate, second signal means for producing a signal which sweeps between said third and fourth frequencies, and connecting means for connecting said first signal means with said second signal means to control the operation of said second signal means at a rate determined by said first signal means signal.
 10. A signal transmitter as in claim 9, in which said second signal means comprises a capacitor, discharging means connected in parallel with said capacitor for discharging said capacitor when the potential across said capacitor reaches a preselected value, a first charging resistor connected between said capacitor and a charging source for causing said capacitor to charge at a selected rate, a second charging resistor, and switch means responsive to said first signal means signal for selectively connecting said second resistor in parallel with said first resistor to change the charging rate of said capacitor.
 11. A signal transmitter as in claim 10, in which said switch means comprises a semiconductor diode. 